There is a desire that a pneumatic radial tire for heavy load vehicles, such as a truck or bus, that is capable of being used on icy and snowy roads will achieve a predetermined driving performance, such as traction performance, in particular while being driven on roads with deep snow, such that the tire is buried in snow reaching the buttress located between the tread and the sidewall.
It has thus been proposed, as in PTL 1, to form for example a plurality of ridges on the buttress surface projecting from the buttress surface and extending in the tire radial direction from the sidewall to the tread edge. The traction performance when driving on snowy roads is improved upon the buttress surface contacting the snow surface due to a traction effect achieved by the ridges with respect to the snow surface, i.e. a so-called edge effect.
In the pneumatic tire disclosed in PTL 1, “the shoulder block has formed thereon a ridge and a square portion, the ridge projecting from the buttress surface in the tire axial direction and including a tapered face on the ground contact side continuous with the ground contact area of the shoulder block, and the square portion including a stepwise tread edge at the front and back of the ridge in the circumferential direction”. According to this pneumatic tire, “when driving in wheel tracks on snowy roads or the like, the opposing force is reduced by the tapered face first aligning with the road surface of the wheel track, and new traction is yielded by the scratching and scraping effect due to the side that faces the direction of travel in the ridge projecting from the buttress surface. Traction is also yielded by the stepwise square portion”.